The photoreceptor cell degeneration resulting from uveitis is a major cause of blindness in the United States and other nations. Previous experimental studies have revealed the importance of inflammatory phagocytes in the initiation of photoreceptor cell degeneration in uveitis. This degeneration appears to be mediated by the phagocyte's release of reactive oxygen species, such as superoxide, at the site of inflammation. However, our preliminary experiments show that in uveitis, the nitric oxide-derived radical peroxynitrite, formed in the presence of superoxide, around the photoreceptor cells could be essential in the initiation of photoreceptor cell degeneration. Moreover, the preliminary results of our studies on uveitis reveal that the nitric oxide-generating enzyme NOS is expressed mainly in the macrophages infiltrating the outer retina rather than in the macrophages infiltrating the uvea, limbal tissue or conjunctiva. Furthermore, the retinal protein arrestin (S-antigen) could induce NOS in macrophages. Based on such novel findings we hypothesize that, in uveitis retinal degeneration is initiated by NOS selective expression in the outer retinal macrophage infiltration and that such NOS expression is induced by retinal soluble proteins. We will test our hypothesis with the following specific aims: 1. Determine the induction of NOS in activated macrophages by S-antigen. 2. Determine the cellular signaling mechanism by which the S-antigen induces NOS in macrophages. 3. Detect the role of NOS products in the initiation of photoreceptor cell degeneration in uveitis. A team of experts has been assembled to undertake this project. Professor Vijay Kalra is an expert in dissecting signaling pathway and protein chemistry. Professor Alex Sevanian is an authority on free radical biology and lipid peroxidation. Dr. Terry D. Lee the director of the core protein sequencing laboratory at City of Hope, Duarte, CA, is an expert on GC/MS and protein sequencing. This team of experts has collaborated with the P.I. in the field of uveitis and other related intraocular inflammations. The principal investigator is experienced in the field of experimental uveitis, free radical biology and GC/MS. The results of this study would elucidate the initial events that lead to retinal degeneration in uveitis and could potentially provide a new therapeutic approach for the prevenation of retinal degenerations in uveitis and related conditions. Abbreviations used in this proposal: GC/MS =gas chromatography-mass spectrometry; LC/MS =liquid chromatrography-mass spectrometry; UV- HPLC=ultraviolet-high pressure liquid chromatrography.